Generally, drinking water is required to be highly purified so that it will not adversely affect those who drink the water for a long period of time. In most developed countries, tap water has reached the standard for purified water. However, there are still many poorer regions in the world with relatively high prevalence rate and mortality rate due to the pollution of the water source, for example, pollutions caused by infectious germs, chemicals, the animal waste, heavy metals and the like.
When the water source at the upper reaches of the river has been polluted by various pollution sources such as dumped waste, industrial emissions, contaminants released to the river as a result of soil erosion, and so on, the polluted water contains various chemicals, infectious viruses and bacteria which may cause various deadly diseases or severe diseases. Long-term drinking of polluted water can cause adverse affects on the human body. Therefore, as a general requirement, the water for drinking should be treated before being supplied for human consumption.
All pollutants contained in the water can be effectively removed by existing water treatment technology. However, the purified water filtered by the water filtration system is generally stored in a water storage tank from which water is extracted for drinking. The purified water can become polluted by airborne pollutants or by other environmental factors while being stored.